The present invention relates to an adapter arrangement for mounting cross-tensioned or pre-tensioned screening media on a screening deck, normally provided with a special sub-frame, and to exchangeable modular screening elements for screening of material, such as crushed stone, gravel or the like.
In mining and stone industries, it is often important to fractionate crushed stone and gravel into fractions of stones with different sizes. Mostly, fractionating is done by supplying an unfractionated stream of crushed stone or gravel to a vibrating screen provided with screening elements having screening holes for allowing stones smaller than the screening holes to pass through the holes.
Today, there are vibrating screens that are manufactured to use only cross-tensioned or pre-tensioned screening media. The cross-tensioned screening media can be either wire mesh screening media or polyurethane/rubber screening media with reinforcement. The pre-tensioned screening media can either be made of a metal sheet or be made of polyurethane/rubber material in a frame with metal reinforcement. The wire mesh screening media has the advantage that it is easy to mount, cheap and has the highest percentage open area.
The cross-tensioned screening media is bought in the desired length and hooks or other fastening means are attached on the two opposite sides of the screen by simple actions. The cross-tensioned screening media is mounted in the vibrating screen with the hooks or the fastening means attached to fastenings means on the side walls of the vibrating screen.
Several support beams are arranged between the side walls of the vibrating screen having their longitudinal direction parallel to the side walls of the vibrating screen. The support beams are arranged at different heights in order to support the cross-tensioned screening media between the side walls of the vibrating screen, causing the cross-tensioned screening media to have a crowned or slightly upwardly curved shape and to support the cross-tensioned or pre-tensioned screening media when being mounted. These vibrating screens have the disadvantage that they are manufactured to only have cross-tensioned screening media, and the wire meshes are not suitable for running larger batches since they have shorter lifetime compared with vibrating screens having screening media made of polyurethane (PU) or rubber.
There are also vibrating screens having screening decks with modular screening elements, e.g. as described in SE-A-0 460 340 (corresponding to U.S. Pat. No. 5,085,324). This document shows a system with modular screening elements in a vibrating screen for screening of crushed rocks or gravel. The vibrating screen according to this document includes a multitude of screening elements. The modular screening elements and cross-tensioned polyurethane/rubber screening media are more expensive than the wire mesh screening media, but they have a longer lifetime. The modular screening elements are, however, supplied from the specific manufacture of the system of modular screening elements and therefore not as easily accessible as the cross-tensioned screening media. There are also manufacturers that deliver specific manufactured modular elements with a pre-tensioned screening media, e.g. the WS 83 module for the WS S5 modular screening system from the company Isenmann. The latter has the disadvantage of being more expensive than cross-tensioned wire mesh.
Another vibrating screen with exchangeable modular screening elements is shown in the Swedish patent application, SE0400337-2, “Screening deck”.
In many cases, especially in the set-up of the vibrating screen, there is a need for running-in the screening deck of the vibrating screen in respect of the size of the screening holes. It might also be the case that a small batch of crushed stones or gravel should be fractionated with a specific size of the holes. In both cases there is a need for a quick, temporary and cheap solution. The cross-tensioned screening media is the best solution in these cases, but the present vibrating screens require to be substantially re-built before can be used with the cross-tensioned screening media if they are of the modular type. If they already are of the cross-tensioned screening media type, they have the disadvantage of not being able to use modular screening elements after the running-in period due to the construction with support beams arranged at different heights.
A difference between wire mesh and the cross-tensioned or the pre-tensioned screening media of polyurethane (PU) or rubber is that the wire mesh provides a larger open area, i.e. an area used for screening. This is caused by the fact that cross-tensioned and pre-tensioned screening media are provided with larger closed areas between the holes to get enough rigidity in the screening media, whereas the wire mesh has enough rigidity in wires forming the wire mesh and need not additional material between holes. The cross-tensioned or the pre- tensioned screening media of polyurethane (PU) or rubber needs also reinforcement material, e.g. wires, incorporated in the polyurethane (PU) or rubber to get enough rigidity.
Faced with the above prior art screening systems and the disadvantages and problems therewith, the object with the present invention is to improve the screening systems in a way that combines the advantages of the system with modular screening elements and the system with cross-tensioned screening media.
Another object of the present invention is to provide a way of providing a vibrating screen with a sub-frame for modular screening elements at the time it is provided with cross-tensioned or pre-tensioned screening media.